Variable pitch propeller



July 14, 1953 E. M. DOUTHETT 2,345,294

VARIABLE Pi'rcl-l 'PROPELLER Filed Oct. '7, 1948 l 5 Sheets-Sheet 1 FIG. I

INVENTOR.

E QNOOD MDOUTHETT MWMM ATTORNEY E. M. DOUTHETT VARIABLE PITCH PROPELLER Jul 14, 1953 5 Sheets-Sheet 2 Filed Oct. 7, 1948 INVENTOR. E L WOOD MDOUTHETT 777m WWW/M ATTORNEY July 14, 1953 E. M. DOUTHETT VARIABLE PITCH PROPELL ER Filed Oct. 7, 1948 5 Sheets-Sheet 3 F8 bSin( A+B) 9200 S (A* B') mmvrozm ELWQOD MDOUTHETT ATTORNEY y 4,1953 I E. M. DOUTHETT 2,645,294

VARIABLE PITCH PROPELL'ER Filed Oct. 7, 1948 5 Sheets-Sheet 5 TAKE OFF RANGE INVENTOR. EgI WOOD MDOUTHETT ATTORNEY Patented July 14 1953 F UNITED? STATES P TENT OFFICE A I .2,e45 ,12 9 .fi VARIABLE PrroH PROPELLER Elwood Douthett, Darby, Pa. Application October 7, 1948, Serial No 53,236

.and descending. Furthermore, it is desirable to ,decrease the blade anglewhen coming in to land,

While maintaining thepropeller instantl adjustable to a smallblade angle should it become necessary to gun the engine in order to avoid obstructions in the landing operation or to. lift the aircraft for a second try at landing.

, Indeed, the best eificiency in propeller construction can only be obtained when proper consideration is given to the independently acting twisting moments on the propeller blade. ward thrust of the craft through amas of air impelsthe blade forward through the air stream. The design of the blade is such as to cause the air stream to setup twisting moments on the blade. These, moments are of least magnitudein low air speed, such as when the craft is on the ground or in a climb. They are of intermediate magnitude when the craft is cruising, and they are of maximum magnitude when the craft is in a dive.

In addition, the operation of the blade itself, independent of the existence of a mass of air,

imposes twisting moments on the. blade." The -.,blade construction being ncnsymmetrical about its longitudinal axis, the centrifugal force set up control; to provide reliable means for continuously varying the blade angle to conformwiththe requirements of operation of the craft through the air mass, which will act independently of the air mass and not be directly affected by the thrust of e the blade through aid mass. This becomes of particular importance when itnisr realized that varying inconsistencies inair masses! present corresponding changes to; the twisting moments externally acting on the propeller whiledthe mo- Thus, the formore fully mentum of the aircraft 2 V maintains a substantially constant forward thrust of the propeller with respect to the air stream.

Moreover, momentary engine difficulties would likewise affect the {speed of the propeller and similarly change the twisting momentsacting there'omwhile the speed of thecraft remains substantially constant. Ineach of these cases, the

i changes of twisting 'moments are momentary on1y,=and it becomes of importance that tendencies of automatic control mechanism to change the pitch to correspond with the flight conditions,

beidelayed at least until the flight requirements Iof the propeller are determined to beof suflicient duration to warrant a change of pitch.

. nAn object of my invention therefore, is to provide a propeller control which varies the propeller pitch ini'a continuous manner to maintain in weffect, a substantially constant angle of attack of thebla'de with respect to the air through which vitpasses, under allcondition of flight; and said rblade employed.

angle of attack automatically coinciding with the .will allow for high engine speeds at lowairspfeeds, R operably to enable high power to be: obtained during: take-01f and climbing conditions.

- A further object of my invention is to provide an automatically controlled variable pitch propellerwhich. is completely reliable in operation 7 and responsive to the requirements of all of the 1 various flight conditions encountered in actual flying operation.

Another'object of my invention isto provide an automatically' controlledvariable pitch propellerwhich automatically neutralizes centrifugal .twisting moments throughout variousstages of A further object of my invention isto provide aneutomatically controlled variable pitch propelle rgof such construction as to permit an op.-

timum of aerodynamic design commensurate with the requirements of the control mechanism,.and

' yetis safe in operation and inexpensive .to construc'tion.

struct and maintain, H

- Another object of my invention is to provide an automatic pitch control mechanism which can be'appliedto already existing aircraft propellers withoutnece'ssitating changesin design or con- A further object of my invention is to provide r 3 specific requirements of any given aircraft engine and propeller.

Other objects of my invention will appear in the more detailed description which follows.

For the purpose of illustrating my invention, I have shown in the accompanying drawings forms thereof which are at present preferred by me, since the same have been found in practice to give satisfactory and reliable results, although it is, to. be understood that the various instrumentalities of which my invention consists can be variously arranged and organized and that my invention is not limited to the precise arrangements and organizationsiofthe;-ins,trumentalities as herein shown and described.

Referring to the drawings in which likerefcrence characters indicate like parts:

Figure 1 represents a plan view, partly in sec-' tion, of a propeller assembly embodying-myinvention,. and for purposes of illustration only, in 1. this. specific zfieur ith long tudin lraxisrofrth :1W mer-We g .a emb risi h wn paralleltot longitudinal axis of thehub.

F u e 2 r p esen i expande vi wx n. p :s ct vehe; rope lem ssembly jiillustrate in :E eurelli'igure 3 represents av :plan view ;of :the ;pro- :zpe lena sem y illustrated in Figure: 1;; andzSh W ,a preferred form f grelationships": betweenr;..the ecounterweight assemblies and the :propeller blades, and includesavector, diagram.

*Fi ure4- representsa transverse sectional view :of .'.a .propeller blade :at u some significant :blade vlstation, showing its relationship-to the; hub and to the counterweightassembly of .aprop'eller as- .:sembly embodying'my.invention,and bearing a :rvector analysis.

:Figure .5 represents afront elevational .view of a propeller; assembly embodying my inven- :;tion,. and incorporating a vector. analysis.

1Figurei6;representsasectional View of aooun- .terweight assembly ofmodified construction; emubodying my invention.

Figure '7 represents a sectionalview of a coun- .terweight assembly of another modified construction, embodying my invention. 7

Figure -8 represents a plan View of a propeller and counterweight .assembly of a further modified constructionwembodying my invention. Figure 9 represents a plan view, partly in sec- .tion of a propeller assembly of another-modified construction embodying my inventionand-illus- .trating the clean aerodynamic surface of the propeller blade, which ismade possible -by=- this modification of my invention.

"Figure :lorepresentsa perspective view of the counterweightv assembly illustrated in'Figure Q.

"Figure ll represents a transverse sectional view of l the propeller blade and counterweight assembly illustrated in Figure-9, and bearing a vectoranalysis.

.Figure 12 represents a development view of apreferred form of a cam track ofa propeller assembly embodying my invention.

M in en mi adaptable fo us u anyntype of propeller assembly; and for pu rposes ofillustrati on only, I amwdescribing it-with respect to a two 7 blade. propeller assembly, --but it is. to be understoodthatitis equallyadaptable for use .in anyassembl-y cra py-number of blades.

Moreover, I am herein illustrating a 'preferred 4 parting from the spirit or essential attributes of my invention.

Thus, I herein provide a propeller assembly having two propeller blades [5 and I6 mounted in a hub H, which in turn is mounted on a conventional type propeller shaft l8. The propeller is mounted in a conventional manner employing a rear cone IS, a split front cone 20, oil seals 2|, propeller retaining nut 22, lock snap ring 23 which protrudes through a slot in the propeller retaining'nut '22 and through a selected hole 24 in the propeller shaft [8 to lock the retaining nut in place. This above explained method of secur- :ing the-propeller is entirely conventional and is employed with many standard propellers in to- :days-"use. The propeller blades l5 and 16 are .free-to twist about their longitudinal axis and are geared together within the hub so that each blade :.will at all times have the same blade angle as the other. This can be accomplished by a gearsegment; 25-- mounted firmly. on the. butt end .qofreach .blade,- .and .with enough .gearsteethi93 to.

mesh with those -of :tl1e:b1'ade synchronizingcgear 1:26 throughout, the range of desired'bladexangles. The: blade synchronizing. gear 26: turns freely'fon :aits,;bearing.= 21, :both ofwhichi are. held in :place by;zthe:bearing retaining 1nuti2 8, which: screws 3.0111301 provided: threaded: portions of: the .already I radial :bearings; 38 -...andv 3 I ,".and thrust bearings 'r32,- which:,are provided for each blade to allow ;the:;bla'des*toiturntfreely; and-blade retaining nuts; 33,: shown .;with suitable locking :means 34,

"hold the .blades firmly withinthe hub. "Theen- :;tire mechanism is preferably lubricated withen- ;gine 'oil;which enters through the conventional hollow propellershaft l8. Oil-sea1s35 and-2| zandthe gasketflfi under'the cover'plate 31 pre- "vent'leakage 0f. the oil. The bladeangle-range rithrough which-the blades can turn about'their' alongitudinal axesis preferably'limited' by ablade iangleastop 38 which is preferably an integral part :ofzthe cover.:plate 31, and-which engages in a ':slot;-3'8a cutinto'the forward side of the blade .tsynchronizing' earn, said slot 38a having a predetermined length and location with respect 30 to: saidxblade anglestop 38 so that when said stop ,form of my -invention,,and it is to beunderstood I 538;.is moved'within said-slot 38a, one end 381) of :the slotz'3Bazswill serve as a limiting stop at the largest :desirabletbla'de angle and prevent move- .zmentaof thestop 38'to a still larger blade-angle; :and the other end-" 380 of the slot 38a will serve :as a limiting stop at the-smallest desirable blade angle-'and .prevent"movement to a still smaller blade angle. Thus the blade angle, referred to :as:.angle AinFiguree, is permitted to vary by rzmovement ;of: the :blade angle-stop'=38 within the 2510i .:38a:and"between the limiting stops-38b and Z38c-thereof; v.the size and location of the blade angle stop 38 and of the slot'38a, as well as the limiting stops 38b and 38c,-being determined for :the particular aircraft engine 'and propeller com- '-,bination for which the-invention isbeing-utilize'd, .as :more fully described hereinafter and further in accordance with accepted propeller practice. It is to be understood that other means of'limitingithe blade angle-may be used without departing from the spirit or essential attributes :of my invention. A spider'arm '39, for mounting :andcentering each of'the'propeller blades I 5 and 16, :projects outwardly along the lateral axis of -atherhub l 'l.

I preferablyform theentire hub l1 and spider arm 39 assembly from one integral forging. This can readily be done, and eliminates difficult centering and balancing procedure occasioned by the use and necessary assembling of a plurality of component parts.

Each blade of the propeller is preferably fitted with two opposedcounterweights, although specific constructions can make it desirable to use one counterweight, or in certain instances, more than two, all without departing from the spirit or essential attributes of this invention. In a preferred form of my invention, I provide a counterweight housing 49, which is made of two halves fitted and clamped to the blade shank by bolts 41 and nuts 42, so that they are rigidly held in place. The counterweight housing preferably comprises a hollow cylindrical interior 54 having an inboard wall 55 and an outboard wall 56. A counterweight 43, which may be of a substantially thick, disc shape ofa diameter slightly less than the internal diameter of the housing 40, is disposed in said housing 40 and adapted when the propeller is at rest, to bear against said inboard wall 55. A helical compression spring 44 is disposed between said counterweight M 43 and said outboard wall 56, and is adapted yieldingly to bear against said counterweight 43 when the latter is urged outwardly because of the action thereon of centrifugal forces imposed by the revolution of said propeller. If desired, the inboard wall 55 may itself be formed on an auxiliary counterweight stop 45 which is machined on one side to fit ontothe circular portion of the housing which is clamped to the I blade shank. Such stops may be held in place by suitable studs and nuts 46. By their use, the position of the counterweight 43 when the propeller is at rest, may be varied by utilizing different sizes of stops 45. A counterweight cap 41 secures the counterweight 43 and counterweight spring 44 within the housing 40.

It will thus be seen that the housing ifl serves as a guide member for the outward movement of the counterweight 43, and the cylindrical wall of the housing serves as a lever through which forces are transmitted from the counterweight to the blade.

In one preferred form of my invention, a small hole 48 drilled through the propeller blade shank and aligned with another hole 49 drilled through the counterweight stops .5 and the housing 40, admits engine lubricating oil intothe interior of the counterweight housing. A gasket 50 under the counterweight cap 4l prevents leakage of this The amount of dampening can be adjusted by varying the amount of this clearance, or by drilling a hole (not shown) of desired size through the counterweight 43.

If desired, the vents 4B and 49 may be omitted,

and the counterweight housing 40 filled. with a selected fluid of any desired viscosity or other characteristic; or the use of a dampening fluid in the counterweight housing 40 .may be dispensed with in cases where such dampening may not be preferred.

As is wellknown in theiscience of aerodynamics, a centrifugal twisting moment exists. in the blades of a rotating propeller. This centrifugal twisting moment develops because the mass of that portion of the blade toward the leading edge and the mass of that portion of the blade toward the trailing edge are not symmetrical with the plane of rotation. The magnitude of this twisting moment is dependent uponthe design of the particular propeller blade chosen and upon the two variables; the propeller speed (R. P. M.) and the blade angle of the propeller. This centrifugal twisting moment of the blade, here designated as MB, is represented schematically in Figure 4 by the two forces F1 acting apart by the perpendicular distance sin A and the magnitude of this twisting moment can be expressed as:

MB:F1 a sin A Here theidistance a is used to represent the fixed distance between the effective centers .of gravity of the mass of that portion of the blade toward the leading edge, and the mass of that portion of the blade toward the trailing edge.

where M is half of that portion of the blademass i that is unsymmetrically distributed, and ii is the speed of the propeller. The centrifugal force I, acting for example through the center of gravity of that unsymmetrical portion of the blade toward the leading edge, will act, at an. angle 3 with respect to the projection of the longitudinal center line of the blade. The. forcecomponent F1 can then be expressed:

F1 7 sin i If the blade angle A. is measured for convenience at that blade station E distance from the center of the hub then:

tan i=sin i= four counterweights 43 with respect to the pro-' peller blades. The counterweights are so arranged that their respective masses are unsym- The angle I A is the blade-angle of the propeller at some sigmetrical with the plane of rotation. This'gives rise to a centrifugal twisting mo'ment-in exact- -'ly the" same manner as did the unsymmetrical' masses of the bladehalves. "In this case, -however, because the-position of the counterweights is of opposite dissymmetry, the twisting moment is opposite to that of the blades.

Figure 5 shows a vector representation of the 9 centrifugal forces'F acting radially outward from the' center of rotation through the center of gravity of eachcounterweight 43. i *can be shown-to have two components. f-The component FA acts parallel to the-longitudinal centerline of the blade and causes the counterwei'ght to bear against the side of the housing.

Each force F The component F0 gives rise to the twisting fmo'ment of the counterweights as is better seen in Figured. The twisting moment-'ofthe counterweights is schematicallyrepresented in Figure 4 by the two forces Fo (one acting from each counterweight) acting apart'bythe perpendiculardistance 2) sin (A-|-B). The centrifugal twisting moment of the counterweights, here designated'as'Mc, can then be expressed:

Mc=Fcb sin (A-I-B) i-Iere 'b. is'the distance between the centersof "gravity of the two counterweights 43. The angle -B is the fixed angle at which the counterweights are set with respect to'the blade angle A. The

force Fe is ,a function of the centrifugalforce on the"counterweights as already explained and is dependent upon both the R. P. M. of the propeller 'and the blade'angle A. V This relationship is here "described mathematically.

Let L be the distance from the center ofiota tion out to the center of gravity 'of the counterweight of mass m. The centrifugal force F developed and acting through the center of gravity of the counterweight can then be expressed:

The centrifugal force F acting radially outward from the center of rotation throughthe center of gravity of the counterweight 43"willact at an angle T with respect to the projection of the longitudinal centerline of the bladeas shown in Figure 5. The force component F'c can then be expressed:

'are subjected to two centrifugal twisting ino- -ments and that each of these moments are dependent upon the same two variables, the speed of the propeller and the blade angle A, in exactly the same relationship. Perhaps this can be "more clearlyseen if it is recalled that the angle Bwill be set at some angle very near 90 degrees.

if forthe purpose of simplicity the angle "B' is set arbitrarily at 90, then:

sin 2'(A+B) =sin (221+ 180) =-sin 2A and.

Mc=1'r' 1v mb sin 2A In consequence it can be understood that given a propeller blade of a chosen design, one skilled in the art could select a counterweight mass such thatthe' two moments MBand Mo would be equal, and the blade would then'experience no twisting moment at the hub. g

The present embodiment of my invention however does not provide that the distance b= should remain constant. Figure 4 shows a vector"rep resentation of the force Fc resolved into two components FE and FD. The component FD causes the counterweight 43 to'be thrust against the spring 44, and thereby cause the spring to deflect. The deflection of the spring 4t gives rise to a variation in the distance b and uniquely results in a governor action on'the propeller which is here described in detail.

The problem of overall efficiency in aircraft design is one of obtaining a desired R. P. M.

of the propeller at a'given forward air speed and a given engine horsepower. A-p roperly designed propeller is one which will give this desired R. P. M. at the most eflicient angle of attack of the blade with respect to the'air; or more generally, at the most efficient blade angle for the given condition. Given these desirable features from already known aircraft, engine, and

propeller characteristics, then a counterweight mass and a counterweight spring can be chosen so that the moment MB and the moment Mo will be equal at this given desirablecondition.

Furthermore if the counterweight. mass and spring are properly chosen, this equilibrium condition of equal twisting moments can be attained so that the spring is subjected to deflection.

With these conditions set up it can be shown that the position of equilibrium will be maintained.

Since the force FD is a function of the centrifugal force on the counterweights and. is dependent upon the R. P. M. of the propeller, then any increase in R. P. M. will increase the force FD and cause an increase in deflection of the springs.

This in turn will result in an increase in the distance b between the counterweights.

If the equilibrium were to be disturbed so that an increase in R. P. M. resulted, both moments Mo and MB would increase, but the moment Mo would increase to a greater degree because of the increase in the distance I) caused by the deflection of the springs. The increase in, the moment Mo over that of themoment MB will cause the -propeller blade to move to a higher pitch,,which would result in slowing the propeller R. P. M. Equilibrium is thus regained.

If the equilibrium were to be disturbed so that a decrease in R. P. M. resulted, both moments Mo and MB would decrease. The moment Mo however would decrease to a greater degree because of the decrease in the distance I) caused by the relaxing of the springs. This would cause the prepeller blades to shift to a lower pitch and result in an increase inthe propeller R. P. M. Equilibrium is thus regained.

7 Hence it can be seen that any tendency to leave theequilibrium-point of the attaineddesired condition would give rise to an sheet that automatically corrects the cause. Should the aircraft be put into a dive, an immediate tendency for the propeller to over-speed would result, but automatically the propeller would shift. to a higher blade angle thus preventing overspeeding. If the attitude of flight were changed to a climb the movable counterweights will prevent under-speeding, by automatically shifting the propeller to a lower pitch.

1 A most necessary feature of all aircraft propellersand propeller controls is that the propeller must allow for high engine R. P. M. during take oif and climb conditions so that high power can be utilized during these periods. With the present invention it has already been established that with low air speeds, any tendency for the propeller to under-speed will be countered by an automatic shift to a lower blade angle. During'take off conditions this blade angle will approach its minimum value as defined by the low pitch blade angle stop. It will be noted by reference to Figures 4 and 5 that as the propeller blade approaches a minimum blade angle the counterweight approaches nearer to the projection of the longitudinal centerline of the blade as illustrated in Figure. 5. In other words, the angle T and. the distance b/2 cos (A+B) becomes very small. This has a twofold effect. First, the force component F0 becomes less effective, as is clarly seen fromthe expression;

2L cos (A+B) This will result in a decreased moment Me which can also be clearly seen from the expression:

F -F sin T= since the angle (A-l-B) must always be greater than 90 to have proper dissymmetry, and that as A decreases the angle (A+B) approaches nearer to 90. Such a decrease in the moment Mo from this first effect will be simultaneous with a decrease in the moment MB since the unsymmetrical blade halves have also become less effective as they approach the plane of rotation. This can be clearly seen since the distance a sin A decreases rapidly as the angle grows small, and also from the expression:

Consequently, from this first effect, both mo.- ments decrease. A secondary eiTect however will also arise from the cmponent FD. This component, is doubly affected since at smaller blade angles it becomes a less important component of the already less effective force Fo. This can readily be seen from the expression:

FD:--FC cos (A-l-B) and:

therefore:

F cos (A +B) Me and. MB equal. Consequently at lower and i 10 lower blade angles the propeller will seek higher and higher R. P. M., so that the force component FD can keep the springs compressed. Another way of expressing this is, that because of the geometry of the arrangement, the strength of the springs hasa greater eiiect at the lower blade angles and requires higher R. P. M. for the maintenance of equilibrium. The invention will then allow for high engine R. P. M. for take of! conditions. Climbing conditions will bring about a desirable intermediate engine speed between that of take oil and that of cruising. The steeper the climb, the slower the air speed, the lower will be the blade angles selected, hence allowing a higher R. P. M. to be utilized.

It is to'be noted that the invention provides for the proper selection of take off and climbing engine speeds by the proper ground adjustment of the angle B in conjunction with the proper. selection of the low pitch blade angle stop. If

limit the take off R. P. M. and the angle B can be adjusted to a still lower value to increase the climbing R. P. M. It must be remembered however than the, angle (A+B) must always be greater than 90 degrees, for if the angle B is set so that at full low pitch the angle (A+B) is less than 90 degrees, the moment Mo will act to assist the moment Me and the propeller will remain in full low pitch.

It follows also that under retarded throttle conditions during approach and landing, underspeeding of the propeller will relax the counter.-

. weight springs and cause the propeller to move to low pitch position. This is desirable since 'sudden applications of high power may be required in the emergency of over-shooting or undershooting the landing strip. 4

It will be noted that this novel counterweight assembly can be immediately appliedto any of the modern day controllable pitch propellers wherein the blades are geared together. This can be done without any changes in design or extensive alteration, simply by properly fitting a by its replacement; or lead washers (not shown) could readily be fitted thereto by any suitable means such as a stud and nut assembly (not shown). Moreover, the position of the counterweight assembly can be adjusted by releasing and resetting the clamps in order to vary the angle B, as has already been mentioned.

In Figure 6 isillustrated a modified construction of counterweight, embodying my invention. Herein, I have constructed the counterweight 43 in a manner to reduce friction between it and the guide member 40. As illustrated, I have provided were herein a plurality of ball races aboutthe.-

cylindrical circumference of the counterweight 43, andadapted to bear against the inner wall orguide member of the housing 40. If desired].

struction embodying my invention, wherein other means are provided for dampening the movement of :the counterweight 43. In this embodiment of my invention, I provide a primary helical compression spring 58 which is disposed under compression between the cap 41 and the counterweight 43. A secondary helical compression spring 59 of preferably smaller diameter is mounted at one end Ell thereof in any suitable retaining means (not shown). disposed on the cap 41, and projects interiorly of the housing 4!} coaxiallyfwith the primary spring 58. The opposed end- 60 of the secondary spring 59fis free and is disposed a pre determined distance from the outboard face 62 of the counterweight 43 when said counterweight 43 is at rest. If desired, a tertiary helical compression spring 63} can be mounted within the housing 40 in a manner similar to the secondary spring 53, and with the' free end 64 of the spring 63 similarly disposed at a pre-determined distance from the outboard face 62 of the counterweight 43. In this manner,; a primary spring load is imposed on the counterweight 43 during the first stage of its outboard impulsi'onfunt'il its outboard face 62 bears against the 'se'condaryfspring 58, whereupon the counterweight isreta'rded'by the additional load imposed onit'by 'sai'dsec'ondary spring 58, This may be consideredthe second stageof the outward impulsion of the counterweight 43, and continues until the outboard face 52 of the counter weight 43 bears against the tertiary spring 63, when it is further additionally retarded by the load of said spring 63. I v r The ratio of counter-twisting moments to pr0- peller twistingmoments can be varied at the desired stages of R. P. Ml; 'or, viewed in another manner, a low blade angle'w'ill be retained until stage, thereby-increasingthe blade angle to the desired degree for the next stage? This will continue as the R P. increases 'until all stages of spring retardation have T been traversed These stages-can be preldt'erminefd by'proper selection of springs and spring lengths.

In Figure 8 is illustratedga further modified In'thisf construction embodying my invention; 7 construction, the longitudinal axis of the cour'i terweight guidemember such that the housing 4U disposed so as to coincide withthe vectorF forany desired blade angle A. Inasmuch as the vector F can be predetermined, the location of f the housing 40 can be selected. In this man-j ner, it is possible further tolreduc'e friction acting ionfthe counterweight."

v Figures 9 to 12 inclusive is illustrated afure ther modified construction embodying my inven-j' tion, whereby the counterweight assembly is embodied interiorly of the hub-blade assembly, thereby to allow a clean aerodynamic'surface on the propeller assembly without retarding the effectiveness of the counterweight operation.

In this embodiment of my invention, and'for l purposes of illustration, I have shown the same been? hu rb d s m l s i l. T@ F1 i t e,

previously shown embodiments of my invention,

although it is to be understood that with but little if any change,.it is equallyadaptable for use in other types of hub-blade assemblies without departing from the spirit or essential attributes of my invention. There are thus provided,

two propeller bladesl5 and IE mounted in a hub I! which in turn is mounted on a conventional type propeller shaft I8, the propeller blades l5 and I6 being free to twist about their longitudinalaxis', and being also geared together within thehub so that each blade will at alltimes have 1 High pitch.

the same bladeangle as the'other. andlow pitch limiting stops arellikewise rerer-, ably provided, and engine lubricating 'oil is also provided for lubrication of the entire mechanism,

all as has been heretofore shown and described forthe embodiment of'my inventionas illustrated,

in Figures l to 5 inclusive.

In the present embodiment of my invention, the counterweight assembly is disposed l within the blade |6,. subs'tantially at the inboard or shank end 66 thereof. For this purpose, the shank end 661 comprises an interior bore 61 extending inev means such as thedowel pins 90, hold the sleeve E8 in fixed relation to the blade [6. An interiorly projecting flange 59 is disposed at the outboard end it Of the sleeve 68,*and is adapted to retain a ballbearing assembly 12 within said sleeve adjacent said outboard end. The bearing 12 is so constructed as tolfit the outboard end 13 of the spider arm 3,9, whileat the same time bearing against the interior of the'sleeve 68.

A suitable spring-retaining means 74 is disposed about the spider arm 39 preferably adjacent the inboard edge of thebearing 'i2l Ina preferred formof assembly, the spring-retaining means 14 comprises a collar whose, outboard edge 75 bears against the inner ball race it of V the bearing 72.

A radial bearing 8i] preferably comprising ball races and ball bearings, is disposed between the inboard end of the sleeve 68 and the spider arm 1 39'. 'A sleeve-likecounterweight H of an in-. ternal diameter slightlyfgreater than the diameter of the spider arm 39, and of an external diameter slightly less than 'the internal diameter of the sleeve 58, is mounted on said spider arm generally adjacent the outbard edge 18 of the inner ball race leiof the bearing SQ. A helical compression spring 89 is interposed between the counterweight fl and the spring-retaining means 14 operably ,to, urge said counterweight toward the inboard end H of the blade it, against the outboard edge [8 of the ball race it. If desired a suitable spring retaining groove 8! may be formed along the outboard fac'e ofgthe counterweight ll.

Suitable keyways 82 are longitudinally disposed along the interior wall of the counterspider arm39 intermediate the bearings l2 and 8ilforj,,if desired, the longitudinalnkeyways may bef formed on thespiden arm and suitable lon,

gitudinal followers or splines maybe formed on. C l

the counterweight. a I

Suitable. cam followers or rollers 84 are mounte ed along the external wall of the counterweight along an axis normal to the longitudinal axis of the counterweight and are secured to said camtracks are as illustrated in Figure 12. Herein, the cam track 85 is shown as having 3 representative stages. The first stage defined by the track 35 following a curve at a substantially large angle to the longitudinal axis. The second stage 8] is defined hythe curve continuing filo.

r the inverse ofthe slope of the cam track, the. angle P being taken with respect to the linear r Thus fromthe. stage 86,. but along a smaller angle with. respect to said axis, The third stage 83 is defined by the cam track 85 continuing from the second stage 8'. but along a still smaller angle with respect to the longitudinal axis. The first stage 36 is indicated in Figure 12 as the Tal;e-.

Oii Range; the second stage 8? is indicated as the Climbing Range; and the third stage. 88 is indicated as the Cruising Range; all as will more fully hereinafter appear.

In operation, when the propeller revolves,

' centrifugal'force imposed on the counterweight i'i impels it outwardly along the spider arm at.

Iii-this outward travel, it rides by means of its keyways, ti -along the splines 83, and is thereby limited tolongitudinal motion along the iii. The cam rollers 84, having their axis fixed with relation to the counterweight "ll, likewise travel only in a direction longitudinal oi the blade i i. Inso doing, the rollers 8Q bear against the side walls of the cam track which is preferably 'formed alon a geometric curve nonparallel to the longitudinal axis of the blade it.

The rollers 85 thus impose a warping or twisting thrust on the cam tracks 85, thereby to rot-ate the sleeve 63 about the longitudinal axis of the spider arm 39. The sleeve 68 being fixed to the blade I5, the blade [6 is thus likewise. rotated I will be equal to. each other.

,pounterweight mass,spring, and angle. P,..-are

the two twisting. moments can be made to occur the center of gravity of'the counterweight, 7c is theforce constant of the spring 89 and. aris the displacement of the springfrom its equilibrium position of no compression. l

The twisting moment due to the counterweight, here. designated as Mo, can be expressed:

Mc =(41r N mrka:)cl cot P where .d is the distance between theoppcsed cam follower 84,;asshown in, Figurejll, and cot Pwis line of, motion of the counterweight '46. i the moment M is made up of two important constituents, one due to the centrifugal force of. the t counterweight (41r N mrd cot P), and one due to the reaction of the spring 89(]c rd cot P) and can-beexpressed; i 1 i r I "f Mei iw Nf mrd cot P-Jcicdcotl The blade twisting moment, MB, has been shown to be expressed by: I

For :any particular; propeller blade design, a

counterweightmass', a spring, and an angle P,

can then be selected sothat duringuany chosen condition of flight, these two twisting moments Further, if the so chosen, this condition of equilibrium between at the particular propeller speed that is most efficient for the airplane,: engine; and propeller 1 1. combination. Once such ail-equilibrium is estab l lished, the, activeforcesaresuch that equilibrium i will be maintained. l

If the equilibrium were to be disturbed so that i l an increase inR. P. M. resu1ted,.both moments about the longitudinal axis of the spider arin 39; The geometric curve is so chosen that the outward travel of the roller thereon will tend to drive the propeller blade toward hi h pitch, and oppose the centrifugal twisting movement of the blades. counterweight fl is resisted by the spring 39, which constantly urges the counterweight toward the inboard end of the blade It.

It will thus be noted that by the action of centrifugal force on the counterweight, the blade angle A tends to be increased; and by the action of the compressionspring; 89, the blade angle A tends 'to be decreased.

When the propeller is rotated, each blade will experience two twisting moments-one, a centrifugal moment of the blades, as has already adequately been described; and two, a centrifugal twisting moment. due to the counterweight H.

The action of centrifugal force on the 1 automatically corrects the cause.

. The net force F acting radially outward at I the counterweight 46 at any given propeller speed N, can be shown to be: r

F=41r N mrka:

' where m is the mass of the counterweight, r is thedistance from the center of rotation out to Mo and MB would increase, but the moment Mo would increase .toa greater degree because of the preponderance of the term 41r N mrd cot P. The increase in M0 over that of MB will cause the counterweight to move outwardlyand the propeller blade to shift to. a higher pitch. This would in turn slow the R. P. M;, and equilibrium would. be regained..- i

If the equilibrium were to be disturbed so that a decrease in R. P. M. resulted, both moments iMc and MB would decrease, but the moment Mo would decrease toa greater degree because of the 1 greater significance ofthe term 41r N mrd' cot P. The counterweight would then move inwardly and the propeller blade would shift to a position .of lower pitch. This'in turn would increase the Therefore it is ascertained that any tendency to leave. the equilibrium point of the attained desired condition would give rise to an eifect which Should the aircraft be put into a dive, an immediate tendency for the propeller to over-speed would result. Automatically, however, the propeller blade would shift to a higher blade angle and thus prevent over-speeding. If the attitude of flight were changed to a climb, themovable counterweights will preventunder-speeding by automatically shifting the blades to a lower pitch.

The invention allowsfor the automatic selection of thedesired propeller speedfor all conditions of flight by the proper design ofthe cam track 85. t Figure 12 shows that the angle P, which made to vary from a. larger value at the inboard be engaged with the inboard portion of the camtrack 85, where the angle P is large in a relative sense. This reduced mechanical advantage would tend to reduce the moment Me, which in turn would necessitate ahigh R.- P. M. for the maintenance of equilibrium. One skilled in" the art can then select the angle Pin accordance with I the other selected and determined veriables so that the desired take-off R. P. M. is attained. As the air speed increases from the condition at take-off,- any tendency for the propeller to overspeed would automatically be combatted -by an increase in the blade angle, and the counterweight rollers 84 would move outward to a differentportion of .the camtrack 85. Theangle- P for. this portion of the cam track could be selectedratrsom'e smaller-value than that-oftake-=-- ofi conditiomior example that forethe climbing condition. 1 Thelincrease. inemechanicals. advantage .(orthe increase in. cot ,P) 1would-tend to: increase .=the ;moment;Mw over thatof- MB and-hence slow the propeller speedrtor that-desiredior clirnbing if theangleP isiproperlylchosenp After the climb. is completed and. theeaircra-ft is levelled: off to a cruising attitudasany tendency for thepropeller to. over-speedwould. again be combatted-by:

an increase in propelller pitch, and the-counter weight rollers. 84.2willtmove outwardly to-a dif-- ferent, position onlthe cam .track85 .wherethe-'- 7 angle P is decreased to that. selectedtvalue which 40 will, give. the desired R. 'P..-M or cruising.- H I For any given condition of flight, =onespecific= blade angle and one specific propeller speed-sis most desirable; Itx' canbeiseen .irom the accompanying drawingsthatthe blade. anglefA .deter- 1. 5

mines the position ofitheirollers B4= on the cam tracks 85. Hence with a determinedscounterwei ht massiandiposition, .a selected ispringi'Bfl; and iwithqlknown. propeller blade characteristics,

the. al eforthe an leRcanbeeasil. determineds u g y "taining means is adiustably secured to said guide which will. 1 give this... most desirable propeller speedsunder -thespecific conditions;

It follows also that=underretarded throttle con-. i.

ditions, during-approach and.1anding,.-.the nden;

speeding of the propeller. will, relax the 7 spring. 89

and the propellerwill movertofulllowrpitch position. This is desirable since sudden applications of high power may-be required in the emergency of undershooting. or .overshootingthe landing strip.

Thus thepresent; embodiment of my invention 4 provides for an automatic pitch ;control :mecha.-; 1; nism,; within the interior of i the. propeller; which =1. can be designed and constructed- .so ,as-tolallowie for; high propellerspeeds for take.-offconditions,..:651

16. bodied in other specific; formswithoutdepartingr, from the spirit or essential attributes thereof, and i I therefore desire the present embodiments ."to

be considered in all respects as illustrativeianding a hub portion; a propeller blade rotatably mounted in said hub :portion to provide pivotal; pitch changing movement of-said blade With-respect to said hub portion; a friction reducing bearing disposed between-said blade and'said hub portion; a variable lever system-attached to said-- blade" to applypitch changing moment thereto; said lever system comprising a'guide member secured to'saidbladeand-projecting laterally therefrom; said guide member protruding fromthe plane of rotation described by said blade during rotation of said propeller assembly; a coun terweight carried by and movably mounted with respectv to said guide member; a retaining means" formed as a portion of said guide member; a yieldable resisting means interposed between counterweight and said retaining means, said yieldable resisting means being engaged with said I counterweight and said retaining means; said counterweight being urged to move along the longitudinal axis of said guide member in response to centrifugal force during rotation of said propeller-assembly, and said counterweight moveing yieldably resisted by said-yieldable 1 means, thereby providing a variable'le- .A variable, pitch propeller assembly as d in claim 1 wherein said guidemember isx stably secured to said blade by a clamping ring:v member to permit circumferential adjustlllfillt Of said guide member with respect to said blade, said clamping ring member being intimate-lyclamped to'said bladeand to said guidemember.

3. A variable pitch propeller assembly as claimed in claim .1 wherein said yieldable resisting means comprises a spring; wherein said remember to permit adjustment of. thetension oi saidspr-ing; wherein said variableleversystemincludes a locking means engaging said. spring retaining means and said guide member tosecur-slylock said spring retaining means in place.

4. A variable pitch propeller assembly. as. claimed in: claim 1 wherein said guide member is constructed-ass closedhollow. cylinder; 'wherein said-counterweight is carried by and movably mounted-within said cylinder, said counterweight having the same cross-sectional shape as said cylinder, said counterweight having a slightly smaller size than the inside ofsaid cylinder;

wherein said yieldable resisting means: is enclosed 1 within said cylinder; wherein said-cy linder is filled with liquid, said liquid being-metered between said counterweight and the inside wall of cylinder in response to movement of said counterweight to provide damping action thereto; said liquid acting as a lubricant to reduce friction between moving component parts of described structure.

5; A variable. pitch propeller. as claimed in claim;l wherein saidyieldable resistingmeans:

comprises a plurality of springs, arranged concentrically with respect to one another and with respect to said guide member, said springs being rigidly secured to said retaining means, said springs being of difierent lengths; said counterweight engaging each spring at different positions along said guide member.

6. A variable pitch propeller assembly as claimed in claim 1 wherein a friction reducing means is interposed between said counterweight and said guide member, said friction reducing means being engaged with said counterweight and said guide member.

7. A variable pitch propeller assembly as claimed in claim 6 wherein a friction reducing means is interposed between said yieldable resisting means andsaid counterweight, said friction reducing means being engaged with said counterweight and said yieldable resisting means.

8. A variable pitch propeller assembly as claimed in claim 1 wherein the longitudinal axis of said guide member is disposed at an angle with respect to the longitudinal axis of said blade, said angle being intermediate the right angle formed by a line perpendicular to the longitudinal axis of said blade at the point of attach- 18 ment of said guide member to said blade, and the zero angle formed by the longitudinal axis of said blade from said point of attachment to the blade tip.

9. A variable pitch propeller assembly as claimed in claim 1, wherein the longitudinal axis of said guide member extends generally perpendicularly from the longitudinal axis of said blade.

ELWOOD M. DOUTHE'IT.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,833,843 Leparmentier Nov. 24, 1931 1,951,321 Blanchard Mar. 13, 1934 2,032,255 Caldwell Feb. 25, 1936 2,139,982 Smith Dec. 13, 1938 2,219,303 Fraser Oct. 29, 1940 2,275,361 Godfrey Mar. 3, 1942 2,294,867 Bottrill Sept. 1, 1942 2,390,733 Perry Dec. 11, 1945 2,416,541 Olman Feb. 25, 1947 2,419,893 Hackethal Apr. 29, 1947 2,427,586 Biermann Sept. 16, 1947 2,435,360 Leiner Feb. 3, 1948 

